Chapter 6 · Watch, then practise
Application Layer
Study DNS as an application protocol with a distributed namespace, delegated authority and cached answers. Trace a lookup and distinguish recursion from a referral.
3 questions · 3 with related videos. Matches are based on playlist titles; broader background matches are labeled.
What to study
- DNS hierarchy
- Recursive and iterative resolution
- Caching and TTL
Chapter playlists
Existing chapter playlist
Notes
Domain Name Server (DNS) Part-1 Explained in Hindi l Computer Network Course
5 Minutes Engineering · 8:10
Choose a video · 2 lectures
DNS lectures support tracing a name lookup.
1. Trace a DNS lookup
On a cache miss, how can a resolver discover the address of www.example.com?
It follows the namespace hierarchy: a root server can refer it to .com servers, which can refer it to the authoritative servers for example.com. The authoritative server supplies the relevant record or another DNS response. Cached delegations can skip some steps.
Domain Name Server (DNS) Part-2 Explained in Hindi l Computer Network Course
5 Minutes Engineering · 7:46 · Background lecture
Choose a video · 2 lectures
DNS lookup background for comparing recursion and referrals.
2. Recursion versus referral
How does a recursive answer differ from a referral?
A server providing recursive service undertakes resolution and returns an answer or error. A nonrecursive response may instead point to a server closer to the requested name. The client or resolver follows that referral itself.
Domain Name Server (DNS) Part-1 Explained in Hindi l Computer Network Course
5 Minutes Engineering · 8:10 · Background lecture
DNS background; the cache-expiry arithmetic is supplied in the written answer.
3. Worked cache lifetime
A record enters a cache at 10:00 with TTL 300 seconds. At 10:04, how much cache lifetime remains?
Sixty seconds remain, assuming ordinary elapsed-time accounting. Once TTL expires at 10:05, this cached copy cannot simply be treated as fresh. TTL limits reuse of cached information; it does not schedule or guarantee an authoritative record change.